1. Field of the Invention
The present invention relates to blood pressure measuring devices, or sphygmomanometers, and, more particularly, to an adjustable deflation valve for a manually inflatable and deflatable blood pressure measuring device.
The measuring of a person's blood pressure, using the auskultatory method of Riva-Rocci, involves the placement of an inflatable measuring cuff around the person's limb and the reading of the cuff pressure at the occurrence of two characteristic changes in the noise which is produced by the arterial blood flow. The established measuring procedure requires the measuring cuff to a pressure under which the blood flow is surpressed and by then slowly reducing the pressure until a first change in noise signals the so-called systolic pressure and, after a further slow reduction of the pressure, a second change in noise signals the so-called diastolic blood pressure level. The two pressure levels having been ascertained, the blood pressure measuring device needs to be completely deflated, before the measuring cuff can be removed from the person's limb.
It has been found that, when using an ordinary deflation valve which is sensitive enough to produce acceptable blood pressure readings, the final deflation of the device takes an inordinate amount of time, as the rate at which air flows out of the measuring cuff decreases exponentially with decreasing pressure.
It has therefore already been suggested that blood pressure measuring devices should be equipped with a deflation valve that has a "dumping" capability, meaning that, while regular actuation of the valve produces the desired slow deflation of the measuring sleeve, a special manipulation of release of the air from the measuring cuff. Advantageously, the deflation valve has a detent capability in its dumping mode, so that the operator need not further attend to the complete evacuation of the air from the measuring cuff, but can perform another task during this time, such as, for example, the recording of the measurements obtained.
Special dual-function valves for this purpose have already been suggested in the past. One such valve is disclosed in my U.S. Pat. No. 4,013,265 which suggests a deflation valve with a pivotably depressible actuating lever which, over a first movement range produces a slow, controlled pressure release and, over a second movement range in the same direction, opens dumping passages in the valve mechanisms. This prior art valve consists essentially of a valve housing with an axial main bore linking the pressure source--an inflation bulb, for instance--to the measuring cuff and pressure gauge. A cross bore in the valve housing leads transversely away from the main bore, in the direction of a pivotable actuating lever. The exit port of this cross bore is a slightly tapered, almost cylindrical valve seat. A matchingly tapered elongated valve plunger extends both ways through this valve seat, the outer extremity of the plunger being engaged by a pivotable actuating lever which, when depressed, pushes the valve plunger into the valve housing, against a spring, thereby opening an annular exit channel around the plunger. The dumping capability is achieved by providing grooves or slots in the valve plunger which, in the normal movement range of the actuating lever, remain outside the range of the valve seat and which, in the dumping position of the actuating lever, provide a greatly increased exit channel across the valve seat.
This prior art deflation valve also suggests a detent mechanism which is capable of retaining the actuating lever in the dumping mode. This detent mechanism may include an upstanding detent member, in the form of either an integral tongue portion of the valve housing or a special leaf spring attached to the valve housing, with a detent extremity which is movable in a radial sense with respect to the pivot axis of the actuating lever. An integral nose portion of the actuating lever, or a detent pin mounted in the lever, moves against the detent extremity of the detent member, as the actuating lever is pivoted about its axis, into its dumping position. The valve may also include a special counter-spring which, by suddenly increasing the movement-opposing bias on the actuating lever, prevents the accidental shift from the normal slow-deflation mode of the valve to the dumping mode.
Another prior art deflation valve with dumping capabilities is disclosed in U.S. Pat. No. 3,738,357. This valve features a valve housing with an axial main bore and a transverse cross bore accommodating a poppet valve controlling an exit port. The poppet valve is operated by means of a depressible actuating cap whose opening displacement is adjustably limited by means of a resettable stop cam, thereby exactly determining the rate of air release during the normal deflation mode. A rotation of the actuating cap about its axis brings the latter out of reach of the stop cam, so that the actuating cap can be further depressed, for the establishment of a dumping mode. In the fully depressed position, the actuating cap jams against the flank of the stop cam, thereby holding this position until the cap is forcibly retracted.
The known prior art deflation valves with dual-mode capability have various shortcomings. In some instances, there have been encountered problems of production tolerances and assembly difficulties, coupled with increased fabrication costs. Other versions are prone to operating problems, especially in connection with the detent mechanism or the jamming and unjamming of the valve actuating member in the dumping mode.